Celery-Root Bisque with Shiitakes

Ingredients

2 lb celery root (sometimes called celeriac), peeled with a knife and cut into 1/2-inch cubes

3 celery ribs, chopped

1/2 lb shallots, chopped

1 stick (1/2 cup) unsalted butter

8 cups water

2 teaspoons salt, or to taste

1/4 teaspoon black pepper, or to taste

1/4 cup heavy cream

1 tablespoon fresh lemon juice, or to taste

6 oz fresh shiitakes, stems discarded and caps sliced 1/4 inch thick

Preparation

Cook celery root, chopped celery, and shallots in 1/2 stick butter in a 5-quart heavy pot over moderate heat, covered, stirring occasionally, until softened but not browned, about 15 minutes. Add water, salt, and pepper and simmer, uncovered, until vegetables are very tender, about 30 minutes.

Purée soup in batches in a blender until smooth (use caution when blending hot liquids), then return to pot.

While bisque is reheating, melt 2 tablespoons butter in a 12-inch heavy skillet over moderately high heat until foam subsides, then sauté mushrooms with salt and pepper to taste, stirring, until golden brown, about 3 minutes. Transfer mushrooms with a slotted spoon to a plate and add remaining 2 tablespoons butter to skillet. Cook butter over moderate heat, swirling skillet, until browned, about 2 minutes, then transfer to
a small bowl.